1. Field of the Invention
This patent relates to an improved nursery container for plants, in particular to a nursery container that provides an improved root structure for plants intended to be transplanted into the ground. This container is constructed of plastic material, preferably post consumer, via a Melt Phase Rotary Thermoforming process or through conventional methods of Thermoforming.
Furthermore this improved nursery container is designed to compensate for material thinning which is a characteristic of all thermoformed products. It also compensates for the limitations placed on nursery container design by the production method of blowmolding plastic containers.
2. Description of the Prior Art
Plants growing in smooth walled plastic containers generally have root systems that quickly grow towards the base of the container. When the roots reach the container base they change direction in response to the lack of an opening. The roots continue to grow, without ample lateral root growth, in a spiral or circular pattern that is well known in the art to be detrimental to plant growth.
This type of growth continues until the roots come into contact with an obstruction and become trapped or until they continue to grow and exit through an opening in the container wall or bottom. Either one or both of these events can contribute to the slowing or termination of root growth. Once the root growth is slowed or terminated, the dominance of the root tip is lost and the development of secondary lateral roots along the length of the root is promoted. While prior art methods have been utilized to discourage spiral and circling root growth, it still occurs and the development of lateral root growth has not been optimized.
An important disadvantage of prior art is that lateral root growth is not promoted until the roots are of a sufficient length to be affected by the container's attributes. In other words, the roots grow for an extended period of time before further lateral root growth is forced by the container's attributes. Subsequently the realization of improved plant health is delayed. Such containers are described in U.S. Pat. No. 4,442,628 issued Apr. 17, 1984; in U.S. Pat. No. 4,497,132 issued Feb. 5, 1985 and in West German Pat. No. DE 4000950 A1 issued Jan. 16, 1989.
The container described in U.S. Pat. No. 3,785,088 issued Jan. 15, 1974 is limited by the loss of growing medium through the holes that extend circumferentially around the pot.
The container described in U.S. Pat. No. 1,775,831 issued Feb. 23, 1927 provides a certain amount of aeration. However it does not provide for a sufficient amount of drainage or irrigation through the small and limited number of drain holes in the bottom. The number and size of these drain holes is limited by the intersection of the inwardly pointing cone's base diameter and the side wall of the container. Furthermore, since the drain holes are limited in number and size, an insufficient amount of openings are presented for the proper air pruning of roots. In addition the smooth interior walls of this container do not discourage spiral or circular root growth.
Other disadvantages of prior art include insufficient aeration and compacting of the growing medium near the center the container's base. Such a container is described in U.S. Pat. No. 4,716,680 issued Jan. 5, 1988. This is also demonstrated by the blowmolded polyethylene nursery containers commonly used by nurseries and sold in retail outlets across the nation. These disadvantages are caused by the flat bottom which is void of drainage and ventilation passages that would deliver and diffuse air into the center of the container to enhance aeration of the growing medium and root system.
Plants have also been grown in bottomless containers placed on either wire mesh or on polyethylene film both placed directly on the ground. Such containers are described in U.S. Pat. No. 5,099,607 issued Mar. 31, 1992 and U.S. Pat. No. 4,939,865 issued Jul. 10, 1990. It is well known in the art that growing plants in bottomless containers is not practical and is used on a limited basis. Such open bottomed containers are not easily moved or shipped to the point of sale without loss of growing medium or damage to the exposed roots.
Another example of prior art is the use of copper-containing compounds applied to the interior of blowmolded nursery containers to inhibit root elongation. While this method is successful, it is an expensive alternative and in most cases is not an economical solution for the correction of spiral and circular root growth.
It is also well known in the art that the previously mentioned inventions are not being mass produced and subsequently are not used in the art. The elaborate features of each design dictate complicated and expensive manufacturing processes that cannot compete economically with the ordinary manufacturing methods of thermoforming, blowmolding and thin-wall injection molding.
It is well known in the art that nursery containers are mass produced via blowmolding. This is accomplished by molding two containers simultaneously, oriented such that the rims of each container face each other so that they are formed and ejected from the mold in the shape of a barrel. This barrel is cut into two parts as a secondary operation, producing two nursery containers. A third operation punches drain holes into the container sidewall near the bottom.
A major disadvantage of blowmolding is that it is limited to the production of relatively smooth, plain and nondescript products that must be free of undercuts. These manufacturing design criteria's impact the nursery container by requiring it to have a flat bottom void of undercuts, contours, shapes or passages that would enhance drainage, aeration and lateral root growth.
Another disadvantage of the blowmolded nursery containers is the failure to have stacking lugs incorporated into the design to prevent the containers from jamming together. This impacts the efficiency of the growers filling operation.
By the present invention an improved nursery container is provided whereby the early development of secondary lateral root growth is encouraged through an improved method of redirecting and air pruning initial root growth. Also, this improved method of air pruning, aeration and drainage are presented through the practical design of a container which permits the efficient mass production of said containers.